System and method for A-GPS positioning of a mobile device

ABSTRACT

A system and method for estimating the position of a mobile device using information from a constellation of satellites. A first set of satellites of the constellation may be selected and then a second set of satellites of the constellation may be selected as a function of signals received from the first set of satellites. Data may be transmitted to the mobile device based on signals received from the second set of satellites, and a location of the device estimated based on the data. One embodiment may select the second set as a function of an intersection of coverage areas of ones of the first set of satellites. Another embodiment may select the second set as a function of one or more satellites that are not occluded by the Earth from one or more of the first set of satellites.

RELATED APPLICATIONS

The instant application claims the priority benefit of U.S. ProvisionalApplication No. 61/012,319, filed Dec. 7, 2007, the entirety of which isincorporated herein by reference.

BACKGROUND

Radio communication systems generally provide two-way voice and datacommunication between remote locations. Examples of such systems arecellular and personal communication system (“PCS”) radio systems,trunked radio systems, dispatch radio networks, and global mobilepersonal communication systems (“GMPCS”) such as satellite-basedsystems. Communication in these systems is conducted according to apre-defined standard. Mobile devices or stations, also known ashandsets, portables or radiotelephones, conform to the system standardto communicate with one or more fixed base stations. It is important todetermine the location of such a device capable of radio communicationespecially in an emergency situation. In addition, the United StatesFederal Communications Commission (“FCC”) has required that cellularhandsets must be geographically locatable by the year 2001. Thiscapability is desirable for emergency systems such as Enhanced 911(“E-911”). The FCC requires stringent accuracy and availabilityperformance objectives and demands that cellular handsets be locatablewithin 100 meters 67% of the time for network based solutions and within50 meters 67% of the time for handset based solutions.

Current generations of radio communication generally possess limitedmobile device location determination capability. In one technique, theposition of the mobile device is determined by monitoring mobile devicetransmissions at several base stations. From time of arrival orcomparable measurements, the mobile device's position may be calculated.However, the precision of this technique may be limited and, at times,may be insufficient to meet FCC requirements. In another technique, amobile device may be equipped with a receiver suitable for use with aGlobal Navigation Satellite System (“GNSS”) such as the GlobalPositioning System (“GPS”). GPS is a radio positioning system providingsubscribers with highly accurate position, velocity, and time (“PVT”)information.

FIG. 1 is a schematic representation of a constellation 100 of GPSsatellites 101. With reference to FIG. 1, GPS may include aconstellation of GPS satellites 101 in non-geosynchronous orbits aroundthe earth. The GPS satellites 101 travel in six orbital planes 102 withfour of the GPS satellites 101 in each plane. Of course, a multitude ofon-orbit spare satellites may also exist. Each orbital plane has aninclination of 55 degrees relative to the equator. In addition, eachorbital plane has an elevation of approximately 20,200 km (10,900miles). The time required to travel the entire orbit is just under 12hours. Thus, at any given location on the surface of the earth withclear view of the sky, at least five GPS satellites are generallyvisible at any given time.

With GPS, signals from the satellites arrive at a GPS receiver and areutilized to determine the position of the receiver. GPS positiondetermination is made based on the time of arrival (“TOA”) of varioussatellite signals. Each of the orbiting GPS satellites 101 broadcastsspread spectrum microwave signals encoded with satellite ephemerisinformation and other information that allows a position to becalculated by the receiver. Presently, two types of GPS measurementscorresponding to each correlator channel with a locked GPS satellitesignal are available for GPS receivers. The two carrier signals, L1 andL2, possess frequencies of 1.5754 GHz and 1.2276 GHz, or wavelengths of0.1903 m and 0.2442 m, respectively. The L1 frequency carries thenavigation data as well as the standard positioning code, while the L2frequency carries the P code and is used for precision positioning codefor military applications. The signals are modulated using bi-phaseshift keying techniques. The signals are broadcast at precisely knowntimes and at precisely known intervals and each signal is encoded withits precise transmission time.

GPS receivers measure and analyze signals from the satellites, andestimate the corresponding coordinates of the receiver position, as wellas the instantaneous receiver clock bias. GPS receivers may also measurethe velocity of the receiver. The quality of these estimates dependsupon the number and the geometry of satellites in view, measurementerror and residual biases. Residual biases generally include satelliteephemeris bias, satellite and receiver clock errors and ionospheric andtropospheric delays. If receiver clocks were perfectly synchronized withthe satellite clocks, only three range measurements would be needed toallow a user to compute a three-dimensional position. This process isknown as multilateration. However, given the engineering difficultiesand the expense of providing a receiver clock whose time is exactlysynchronized, conventional systems account for the amount by which thereceiver clock time differs from the satellite clock time when computinga receiver's position. This clock bias is determined by computing ameasurement from a fourth satellite using a processor in the receiverthat correlates the ranges measured from each satellite. This processrequires four or more satellites from which four or more measurementscan be obtained to estimate four unknowns x, y, z, b. The unknowns arelatitude, longitude, elevation and receiver clock offset. The amount b,by which the processor has added or subtracted time is the instantaneousbias between the receiver clock and the satellite clock. It is possibleto calculate a location with only three satellites when additionalinformation is available. For example, if the elevation of the handsetor mobile device is well known, then an arbitrary satellite measurementmay be included that is centered at the center of the earth andpossesses a range defined as the distance from the center of the earthto the known elevation of the handset or mobile device. The elevation ofthe handset may be known from another sensor or from information fromthe cell location in the case where the handset is in a cellularnetwork.

Traditionally, satellite coordinates and velocity have been computedinside the GPS receiver. The receiver obtains satellite ephemeris andclock correction data by demodulating the satellite broadcast messagestream. The satellite transmission contains more than 400 bits of datatransmitted at 50 bits per second. The constants contained in theephemeris data coincide with Kepler orbit constants requiring manymathematical operations to turn the data into position and velocity datafor each satellite. In one implementation, this conversion requires 90multiplies, 58 adds and 21 transcendental function cells (sin, cos, tan)in order to translate the ephemeris into a satellite position andvelocity vector at a single point, for one satellite. Most of thecomputations require double precision, floating point processing.

Thus, the computational load for performing the traditional calculationis significant. The mobile device must include a high-level processorcapable of the necessary calculations, and such processors arerelatively expensive and consume large amounts of power. Portabledevices for consumer use, e.g., a cellular phone or comparable device,are preferably inexpensive and operate at very low power. These designgoals are inconsistent with the high computational load required for GPSprocessing.

Further, the slow data rate from the GPS satellites is a limitation. GPSacquisition at a GPS receiver may take many seconds or several minutes,during which time the receiver circuit and processor of the mobiledevice must be continuously energized. Preferably, to maintain batterylife in portable receivers and transceivers such as mobile cellularhandsets, circuits are de-energized as much as possible. The long GPSacquisition time can rapidly deplete the battery of a mobile device. Inany situation and particularly in emergency situations, the long GPSacquisition time is inconvenient.

Assisted-GPS (“A-GPS”) has gained significant popularity recently inlight of stringent time to first fix (“TTFF”), i.e., first positiondetermination, and sensitivity, requirements of the FCC E-911regulations. In A-GPS, a communications network and associatedinfrastructure may be utilized to assist the mobile GPS receiver, eitheras a standalone device or integrated with a mobile station or device.The general concept of A-GPS is to establish a GPS reference network(and/or a wide-area D-GPS network) including receivers with clear viewsof the sky that may operate continuously. This reference network mayalso be connected with the cellular infrastructure, may continuouslymonitor the real-time constellation status, and may provide data foreach satellite at a particular epoch time. For example, the referencenetwork may provide the ephemeris and the other broadcast information tothe cellular infrastructure. In the case of D-GPS, the reference networkmay provide corrections that can be applied to the pseudoranges within aparticular vicinity. As one skilled in the art would recognize, the GPSreference receiver and its server (or position determination entity) maybe located at any surveyed location with an open view of the sky.

However, the signal received from each of the satellites may notnecessarily result in an accurate position estimation of the handset ormobile device. The quality of a position estimate largely depends upontwo factors: satellite geometry, particularly, the number of satellitesin view and their spatial distribution relative to the user, and thequality of the measurements obtained from satellite signals. Forexample, the larger the number of satellites in view and the greater thedistances therebetween, the better the geometry of the satelliteconstellation. Further, the quality of measurements may be affected byerrors in the predicted ephemeris of the satellites, instabilities inthe satellite and receiver clocks, ionospheric and troposphericpropagation delays, multipath, receiver noise and RF interference.

A-GPS implementations generally rely upon provided assistance data toindicate which satellites are visible. As a function of the assistancedata, a mobile device will attempt to search for and acquire satellitesignals for the satellites included in the assistance data. A-GPSpositioning may also rely upon the availability of a coarse locationestimate to seed the positioning method. This coarse estimate may beutilized to determine a likely set of satellites from which a respectivemobile device may receive signals. In the absence of a location estimateor in scenarios having a location estimate with a large uncertainty, thelikely set of measurable satellites may be quite large. Further, each ofthese satellites may not be measurable (e.g., the satellite is no longervisible, etc.). If satellites are included in the assistance data thatare not measurable by the mobile device, then the mobile device willwaste time and considerable power attempting to acquire measurements forthe satellite. Further, signaling methods often limit the number ofsatellites for which signals may be provided.

Accordingly, there is a need for a method and apparatus for geographiclocation determination of a device that would overcome the deficienciesof the prior art. Therefore, an embodiment of the present subject matterprovides a method for determining the location of a wireless device. Themethod comprises the steps of determining a first plurality ofsatellites for a region in which the wireless device is located anddetermining a second plurality of satellites as a function of anintersection of coverage areas of ones of the first plurality ofsatellites. Assistance data may be transmitted to the device thatincludes information from the second plurality of satellites. A locationof the device may then be estimated from the information. In anotherembodiment of the present subject matter, the determination of the firstplurality of satellites may be iteratively repeated until the number ofsatellites is equal to or greater than a predetermined threshold.

Another embodiment of the present subject matter provides a furthermethod for determining the location of a wireless device. The methodcomprises the steps of determining a first set of satellites for aregion in which the wireless device is located and determining a secondset of satellites as a function of one or more satellites that are notoccluded by the Earth from one or more of the first set of satellites.Assistance data may be transmitted to the device that includesinformation from the second set of satellites. A location of the devicemay then be estimated from the information. In another embodiment of thepresent subject matter, the determination of the first set of satellitesmay be iteratively repeated until the number of satellites is equal toor greater than a predetermined threshold.

A further embodiment of the present subject matter provides a system fordetermining a location of a device from signals received from aplurality of GNSS satellites. The system may comprise circuitry fordetermining a first plurality of satellites for a region in which adevice is located and circuitry for determining a second plurality ofsatellites as a function of an intersection of coverage areas of ones ofthe first plurality of satellites. The system may further include atransmitter for transmitting assistance data to the device where theassistance data may include information from the second plurality ofsatellites. The system may also include circuitry for estimating alocation of the device from the information.

An additional embodiment of the present subject matter provides a systemfor determining a location of a device from signals received from aplurality of GNSS satellites. The system may comprise circuitry fordetermining a first set of satellites for a region in which the deviceis located and circuitry for determining a second set of satellites as afunction of one or more satellites that are not occluded by the Earthfrom one or more of the first set of satellites. The system may furtherincludes a transmitter for transmitting assistance data to the devicewhere the assistance data may include information from the second set ofsatellites. The system may also include circuitry for estimating alocation of the device from the information.

One embodiment of the present subject matter provides a method forestimating the position of a mobile device using information from aconstellation of satellites. The method may comprise receiving firstinformation from a first set of satellites of the constellation andreceiving second information from a second set of satellites of theconstellation where the second set is selected based on the firstinformation. Data may then be transmitted based on the secondinformation to the device, and a location of the device estimated basedon the data.

Yet another embodiment of the present subject matter provides a methodfor estimating the position of a mobile device using information from aconstellation of satellites. The method may comprise selecting a firstset of satellites of the constellation and selecting a second set ofsatellites of the constellation as a function of first signals receivedfrom the first set of satellites. Data may be transmitted to the devicebased on second signals received from the second set of satellites, anda location of the device estimated based on the data.

A further embodiment of the present subject matter provides a method fordetermining the location of a wireless device. The method may comprisedetermining a first set of satellites for a region in which the wirelessdevice is located and transmitting assistance data to the deviceincluding information from the first set of satellites. The method mayfurther comprise attempting to measure any one or plural signalstransmitted from one or more satellites in the first set and determininga second set of satellites as a function of the first signals receivedfrom the first set of satellites. Assistance data may then betransmitted to the device that includes information from the second setof satellites. The method may further comprise attempting to measure oneor plural signals transmitted from one or more satellites in the secondset and estimating a location of the device from the second signals.

In one embodiment of the present subject matter, there is nointersection between the first set and second set of satellites. Ofcourse, in other embodiments any number of satellites may be commonbetween the sets. Exemplary data may be assistance data. In oneembodiment of the present subject matter, the second set may be selectedas a function of coverage areas of the first signals from ones of thefirst set of satellites; and in another embodiment, the second set maybe selected as a function of one or more satellites that are notoccluded by the Earth from the first signals from ones of the first setof satellites. In another embodiment, the method may iteratively repeatthe steps represented by blocks 1040 through 1060 until the second setof satellites is equal to or greater than a predetermined threshold. Ofcourse, any one or plural measurements of the second signals during thisiterative procedure may be combined to meet the predetermined threshold.Another embodiment may also suppress transmissions of any assistancedata during the procedure if the assistance data was previously providedto the device. Yet another embodiment of the present subject matter mayinclude more or less satellites in the second set as a function ofsatellite elevation.

These embodiments and many other objects and advantages thereof will bereadily apparent to one skilled in the art to which the inventionpertains from a perusal of the claims, the appended drawings, and thefollowing detailed description of the embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a constellation of GPSsatellites.

FIG. 2 is a depiction of one method of selecting a second plurality ofsatellites according to an embodiment of the present subject matter.

FIG. 3 is a depiction of another method of selecting a second pluralityof satellites according to an embodiment of the present subject matter.

FIG. 4 is an algorithm according to one embodiment of the presentsubject matter.

FIG. 5 is another algorithm according to one embodiment of the presentsubject matter.

FIG. 6 is an additional algorithm according to one embodiment of thepresent subject matter.

FIG. 7 is a further algorithm according to one embodiment of the presentsubject matter.

FIG. 8 is a system according to one embodiment of the present subjectmatter.

FIG. 9 is a schematic representation for implementing one embodiment ofthe present subject matter.

FIG. 10 is another algorithm according to one embodiment of the presentsubject matter.

DETAILED DESCRIPTION

With reference to the figures where like elements have been given likenumerical designations to facilitate an understanding of the presentsubject matter, the various embodiments of a system and method for A-GPSpositioning of a mobile device are herein described.

The disclosure relates to methods and apparatuses for determininggeolocation using satellite signals and assistance data. The satellitesmay be considered as part of a Global Navigation Satellite System(“GNSS”), such as, but not limited to, the U.S. Global PositioningSystem (“GPS”). While the following description references the GPSsystem, this in no way should be interpreted as limiting the scope ofthe claims appended herewith. As is known to those of skill in the art,other GNSS systems operate, for the purposes of this disclosure,similarly to the GPS system, such as, but not limited to, the EuropeanSatellite project, Galileo; the Russian satellite navigation system,GLONASS; the Japanese Quasi-Zenith Satellite System (“QZSS”), and theChinese satellite navigation and positioning system called Beidou (orCompass). Therefore, references in the disclosure to GPS and/or GNSS,where applicable, as known to those of skill in the art, apply to theabove-listed GNSS systems as well as other GNSS systems not listedabove.

Generally wireless A-GPS devices or handsets have a low time to firstfix (“TTFF”) as the devices are supplied with assistance data from anexemplary communications network to assist in locking onto or acquiringsatellites quickly. Exemplary network elements that supply theassistance data may be a Mobile Location Center (“MLC”) or othercomparable network element.

Typical A-GPS information includes data for determining a GPS receiver'sapproximate position, time synchronization mark, satellite ephemerides,and satellite dopplers. Different A-GPS services may omit some of theseparameters; however, another component of the supplied information isthe identification of the satellites for which a device or GPS receivershould search. The MLC generally determines this information utilizingan approximate location of the device. Conventionally, this approximatelocation may be the location of the cell tower serving the device. TheMLC may then supply the device with the appropriate A-GPS assistancedata for the set of satellites in view from this conventional location.

This typical process performs well when the approximate locationpossesses a small uncertainty; however, in the absence of an approximatelocation or where the approximate location possesses a large uncertainty(e.g., an uncertainty measured in hundreds of kilometers) the possibleset of satellites may be quite large, and not all of the satellites inthis set may be measurable. As each satellite requires time andresources to provide assistance data therefor and signaling methodsoften limit the number of satellites for which signals may be provided,assistance data for only a subset of the set satellites may be providedto the mobile device.

Since A-GPS implementations generally rely upon the provided assistancedata to indicate which satellites are visible, the mobile deviceattempts to acquire only the satellite signals for the satellitesincluded in the assistance data. In the absence of a location estimate,a small number of the satellites included in the assistance data may bemeasurable for the mobile device resulting in no location fix or a poorquality location fix of the respective device.

Embodiments of the present subject matter may utilize a staged approachto determine a plurality or set of satellites to select and send to amobile device. In one embodiment of the present subject matter a widespread of satellites may be selected to ensure an even coverage over apredetermined location, such as, but not limited to, the entire planetor the entirety of the known area of the location estimate, e.g., cell,communications network, city, county, country, continent, etc.

After this selection of satellites, generally one of four outcomes mayoccur: (i) the device may be able to determine its respective locationwith adequate precision from available satellite measurements; (ii) thedevice may be able to provide a rough location estimate with apredetermined number of satellite measurements, but the locationestimate may not adequately precise or possesses a poor quality. Forexample, methods utilizing an earth-centered pseudo-measurement may beemployed with three satellite measurements, even with an inadequateprecision; standard A-GPS methods may then be employed to determineanother set of satellites for which signals may be provided to thedevice. The remaining outcomes may be that (iii) the device may be ableto provide one or two satellite measurements (in this instance, alocation estimate may not be determined, however, the satellitemeasurements may be utilized to select another plurality or set ofsatellites for which assistance data may be provided or that are morelikely to produce additional satellite measurements); and (iv) nosatellite measurements are obtained, whereby the aforementioned processmay be reattempted with a different set of satellites, or abandoned.

In the scenarios where a second plurality or set of satellites may bedetermined or selected, embodiments of the present subject matter mayprovide various methods for such a selection. For example, in oneembodiment of the present subject matter, a second plurality or set ofsatellites may be selected as a function of an intersection of thecoverage areas of the first plurality of satellites whereby thisintersection may be employed as the new reference location. FIG. 2 is adepiction of one method of selecting a second plurality of satellitesaccording to an embodiment of the present subject matter. With referenceto FIG. 2, a first satellite 201 and a second satellite 202 may bepresent in the first plurality or set of satellites. Of course, anynumber of satellites may be present in the first plurality or set ofsatellites and the depiction of two satellites in FIG. 2 should not inany way limit the scope of the claims herewith as this depiction isprovided for ease of description. The first satellite 201 provides afirst coverage area 211 projected upon the surface of the Earth 250. Thesecond satellite 202 provides a second coverage area 212 projected uponthe surface of the Earth 250. An intersection area 220 of these tworespective coverage areas 211, 212 may be employed as a referencelocation or estimated location for which a second set or plurality ofsatellites is determined. In a further embodiment of the present subjectmatter, the coverage area may be extended or decreased by apredetermined amount or area to thereby increase or reduce the number ofsatellites in the second plurality or set of satellites.

In another embodiment of the present subject matter, a second pluralityor set of satellites may be selected as a function of an occlusion maskdrawn from each measured satellite. FIG. 3 is a depiction of anothermethod of selecting a second plurality of satellites according to anembodiment of the present subject matter. With reference to FIG. 3,signals from a first satellite 301 and a second satellite 302 in a firstplurality of satellites may be measured by a device. The first pluralityof satellites may be any number or all of the satellites 301, 302, 303,304, 305 in a satellite constellation. In the scenario depicted by FIG.3, an occlusion mask 311, 312 may be drawn from any one or more measuredsatellites 301, 302 (it should be noted that in three-dimensions, theocclusion masks 311, 312 are conical). Satellites 304, 305 may then beremoved from a second plurality or set of satellites provided in futureassistance data if any one or more of the satellites are occluded by theEarth 350 from any one or more measured satellites 301, 302. Asillustrated, three satellites 305 are occluded by the Earth 350 fromboth measured satellites 301, 302, and four satellites 304 are occludedby the Earth 350 from one of the measured satellites 301 or 302. Thisillustration is exemplary only and should not in any way limit the scopeof the claims appended herewith. Any set or subset of the remainingsatellites 301, 302, 303 may then be selected for the second pluralityof satellites.

In a further embodiment of the present subject matter, the respectiveocclusion masks 311, 312 may be extended or decreased by a predeterminedamount or angle to thereby alter the conical mask to increase or reducethe number of satellites in the second plurality or set of satellites.For example, an exemplary occlusion mask may be extended if the mobiledevice is unable to measure satellites below a certain angle above thehorizontal. Additionally, an exemplary occlusion mask may be decreasedif the mobile device is able to measure satellites at a certain anglebelow the horizontal.

In one embodiment of the present subject matter the first and secondplurality of satellites may be mutually exclusive, that is, there maynot be a satellite of the first plurality of satellites that is a memberof the second plurality of satellites; therefore, the associatedassistance data would also be mutually exclusive. Of course, embodimentsof the present subject matter may include one or more common satellitesin each of the first and second plurality or sets of satellites,especially in the instance where the mobile device was able to provide ameasurement for the common satellite.

FIG. 4 is an algorithm according to one embodiment of the presentsubject matter. With reference to FIG. 4, a method for determining thelocation of a wireless device is provided. An exemplary wireless devicemay be a cellular device, text messaging device, computer, portablecomputer, vehicle locating device, vehicle security device,communication device, or wireless transceiver. At block 410, a firstplurality of satellites may be determined for a region in which thewireless device is located. In one embodiment of the present subjectmatter, block 410 may be iteratively repeated until the first pluralityof satellites is equal to or greater than a predetermined threshold. Thesatellites may be part of a GNSS, such as, but not limited to, GPS,Galileo, GLONASS, and QZSS. The region in which the wireless device islocated may be, but is not limited to, a serving area of a base stationserving the wireless device, an approximate area of a communicationsnetwork, a city, a municipality, a county, a state, a country, acontinent, or the Earth.

A second plurality of satellites may then be determined at block 420 asa function of an intersection of coverage areas of ones of the firstplurality of satellites. Assistance data may then be transmitted to thedevice including information from the second plurality of satellites atblock 430, and a location of the device estimated from the informationat block 440. Of course, the estimated location of the device may alsobe determined as a function of signals provided by an exemplary cellularnetwork and/or may be determined as a function of a pseudo-measurement.In an alternative embodiment of the present subject matter, no satelliteof the first plurality of satellites may be a member of the secondplurality of satellites, that is, the sets of satellites are mutuallyexclusive. Of course, in other embodiments of the present subject matterany number of satellites may also be common between the first and secondplurality of satellites. In another embodiment of the present subjectmatter more or less satellites may be included in the second pluralityas a function of satellite elevation.

FIG. 5 is another algorithm according to one embodiment of the presentsubject matter. With reference to FIG. 5, a method for determining thelocation of a wireless device is provided. An exemplary wireless devicemay be a cellular device, text messaging device, computer, portablecomputer, vehicle locating device, vehicle security device,communication device, or wireless transceiver. At block 510, a first setof satellites may be determined for a region in which the wirelessdevice is located. In one embodiment of the present subject matter,block 510 may be iteratively repeated until the first set of satellitesis equal to or greater than a predetermined threshold. The satellitesmay be part of a GNSS, such as, but not limited to, GPS, Galileo,GLONASS, and QZSS. The region in which the wireless device is locatedmay be, but is not limited to, a serving area of a base station servingthe wireless device, an approximate area of a communications network, acity, a municipality, a county, a state, a country, a continent, or theEarth.

A second set of satellites may then be determined at block 520 as afunction of one or more satellites that are not occluded by the Earthfrom one or more of the first set of satellites. In a further embodimentof the present subject matter, block 520 may further comprise includingmore or less satellites in the second set as a function of satelliteelevation. Assistance data may then be transmitted to the deviceincluding information from the second set of satellites at block 530,and a location of the device estimated from the information at block540. Of course, the estimated location of the device may also bedetermined as a function of signals provided by an exemplary cellularnetwork and/or may be determined as a function of a pseudo-measurement.In an alternative embodiment of the present subject matter, there is nointersection between the first set and second set of satellites. Ofcourse, in other embodiments of the present subject matter any number ofsatellites may be common between the sets.

FIG. 6 is an additional algorithm according to one embodiment of thepresent subject matter. With reference to FIG. 6, a method forestimating the position of a mobile device using information from aconstellation of satellites is provided. An exemplary mobile device maybe a cellular device, text messaging device, computer, portablecomputer, vehicle locating device, vehicle security device,communication device, or wireless transceiver. The satellites may bepart of a GNSS, such as, but not limited to, GPS, Galileo, GLONASS, andQZSS. At block 610, first information from a first set of satellites ofthe constellation may be received, and at block 620 second informationfrom a second set of satellites of the constellation may be receivedwhere the second set of satellites is selected based on the firstinformation. Data may then be transmitted to the device based on thesecond information at block 630, and a location of the device estimatedbased on the data at block 640. In one embodiment of the present subjectmatter, there is no intersection between the first set and second set ofsatellites. Of course, in other embodiments any number of satellites maybe common between the sets. Exemplary data may be assistance data. Inanother embodiment of the present subject matter, the first informationmay include coverage areas of ones of the first set of satellites; andin another embodiment, the first information may include whether one ormore of the first set of satellites are occluded by the Earth from oneor more of the second set of satellites.

FIG. 7 is a further algorithm according to one embodiment of the presentsubject matter. With reference to FIG. 7, a method for estimating theposition of a mobile device using information from a constellation ofsatellites is provided. An exemplary mobile device may be a cellulardevice, text messaging device, computer, portable computer, vehiclelocating device, vehicle security device, communication device, orwireless transceiver. The satellites may be part of a GNSS, such as, butnot limited to, GPS, Galileo, GLONASS, and QZSS. At block 710, a firstset of satellites of the constellation may be selected and at block 720,a second set of satellites of the constellation may be selected as afunction of first signals received from the first set of satellites. Atblock 730, data may be transmitted to the device data based on secondsignals received from the second set of satellites. Then, at block 740,a location of the device may be estimated based on the data. In oneembodiment of the present subject matter, there is no intersectionbetween the first set and second set of satellites. Of course, in otherembodiments any number of satellites may be common between the sets.Exemplary data may be assistance data. In one embodiment of the presentsubject matter, the second set may be selected as a function of coverageareas of the first signals from ones of the first set of satellites; andin another embodiment, the second set may be selected as a function ofone or more satellites that are not occluded by the Earth from the firstsignals from ones of the first set of satellites.

FIG. 8 is a system according to one embodiment of the present subjectmatter. With reference to FIG. 8, a system 800 for determining alocation of a device from signals received from a plurality of GNSSsatellites may include, as represented at block 810, circuitry fordetermining a first plurality or set of satellites for a region in whicha device is located. The GNSS may be, but is not limited to GPS,Galileo, GLONASS, or QZSS. Exemplary wireless devices may be a cellulardevice, text messaging device, computer, portable computer, vehiclelocating device, vehicle security device, communication device, orwireless transceiver.

In one embodiment the system may include circuitry for determining asecond plurality of satellites as a function of an intersection ofcoverage areas of ones of the first plurality of satellites at block820. In another embodiment the system may include circuitry fordetermining a second set of satellites as a function of one or moresatellites that are not occluded by the Earth from one or more of thefirst set of satellites at block 822. The system may also include atransmitter for transmitting assistance data to the device includeinformation from the second plurality or set of satellites, representedby block 830, and the system may include, as represented by block 840,circuitry for estimating a location of the device from the information.In one embodiment of the present subject matter the first and secondplurality of satellites may be mutually exclusive or there is nointersection between the first or second sets of satellites. Of course,the estimated location of the device may also be a function of signalsprovided by a cellular network and/or may be a function of apseudo-measurement. In an alternative embodiment of the present subjectmatter, the system may include circuitry for including more or lesssatellites in the second set or plurality as a function of satelliteelevation.

FIG. 9 is a schematic representation for implementing one embodiment ofthe present subject matter. With reference to FIG. 9, a satellite system910 communicates with a ground system 920. The ground system 920 mayinclude a cellular network having a location center 921. The locationcenter 921 may be a Mobile Location Center (MLC) or a central officeconfigured to communicate with a telecommunication network 922 and atleast one base station 923. In one embodiment of the present subjectmatter, a device 924 communicates with the base station 923 to acquireGPS assistance data. For example, the location center 921 may or may notreceive a preliminary estimate of the receiver's location or boundarythereof on the basis of the receiver's cell site or other area, such asthe boundary of the communications network or an area or region such as,but not limited to, city, municipality, county, state, country, orcontinent. The location center 921 may also determine a plurality ofsatellites as a function of this boundary or region and determinewhether any one or more of these plural satellites, while operational,are not visible by the device 924 for some reason. The location center921 may also receive satellite information from GPS satellites. Thesatellite information may include the satellite's broadcast ephemerisinformation of the broadcasting satellite or that of all satellites orthat of selected satellites. Further, the location center 921 maymanipulate the assistance data to prevent the device 924 from searchingand attempting to acquire signals from these one or more pluralsatellites. This information may then be transmitted or relayed to themobile receiver and utilized for location determination. The locationcenter 921 may relay the information back to the device 924 or use theinformation, either singularly or along with some preliminary estimationof the device's location, to assist the device in a geographic locationdetermination. In another embodiment, any one or plural stepsillustrated in FIGS. 2-7 may be implemented at the location center 921and communicated to the device 924. Of course, the estimated location ofthe device 924 may be determined as a function of additional signalsprovided by the network 922. Exemplary devices may be, but are notlimited to, a cellular device, text messaging device, computer, portablecomputer, vehicle locating device, vehicle security device,communication device, and wireless transceiver.

FIG. 10 is another algorithm according to one embodiment of the presentsubject matter. With reference to FIG. 10, a method for determining thelocation of a wireless device 1000 is provided. An exemplary mobiledevice may be a cellular device, text messaging device, computer,portable computer, vehicle locating device, vehicle security device,communication device, or wireless transceiver. The method may comprisedetermining a first set of satellites for a region in which the wirelessdevice is located at step 1010. The satellites may be part of a GNSS,such as, but not limited to, GPS, Galileo, GLONASS, and QZSS. Exemplaryregions may be, but are not limited to, a serving area of a base stationserving the wireless device, an approximate area of a communicationsnetwork, a city, a municipality, a county, a state, a country, acontinent, and the Earth. At step 1020, assistance data may betransmitted to the device that includes information from the first setof satellites. An attempt at measuring any signal transmitted from oneor more satellites in the first set may be employed at step 1030. Asecond set of satellites may then be determined as a function of thefirst signals received from the first set of satellites at step 1040. Atstep 1050, assistance data may be transmitted to the device thatincludes information from the second set of satellites. An attempt atmeasuring any signal transmitted from one or more satellites in thesecond set may be conducted at step 1060. In one embodiment of thepresent subject matter, the device may not attempt to measure one ormore satellites in the first set already possessing a measured firstsignal. At step 1070, a location of the device may be estimated from thesecond signals. In another embodiment the location may also be estimatedas a function of a pseudo-measurement.

In one embodiment of the present subject matter, there is nointersection between the first set and second set of satellites. Ofcourse, in other embodiments any number of satellites may be commonbetween the sets. Exemplary data may be assistance data. In oneembodiment of the present subject matter, the second set may be selectedas a function of coverage areas of the first signals from ones of thefirst set of satellites; and in another embodiment, the second set maybe selected as a function of one or more satellites that are notoccluded by the Earth from the first signals from ones of the first setof satellites. In another embodiment, the method may iteratively repeatthe steps represented by blocks 1040 through 1060 until the second setof satellites is equal to or greater than a predetermined threshold. Ofcourse, any one or plural measurements of the second signals during thisiterative procedure may be combined to meet the predetermined threshold.Another embodiment may also suppress transmissions of any assistancedata during the procedure if the assistance data was previously providedto the device. Yet another embodiment of the present subject matter mayinclude more or less satellites in the second set as a function ofsatellite elevation.

It is therefore an aspect of embodiments of the present subject matterto improve the probability of successfully utilizing A-GPS to determinea position of a mobile device in the absence of a location estimate orin the absence of a quality location estimate.

It is also an aspect of the embodiments of the present subject matter tolimit the amount of time that a mobile device spends in acquiringsatellite signals thereby providing a greater probability of successthan many other A-GPS methods.

As shown by the various configurations and embodiments illustrated inFIGS. 1-10, a method and system for A-GPS positioning of a mobile devicehave been described.

While preferred embodiments of the present subject matter have beendescribed, it is to be understood that the embodiments described areillustrative only and that the scope of the invention is to be definedsolely by the appended claims when accorded a full range of equivalence,many variations and modifications naturally occurring to those of skillin the art from a perusal hereof.

1. A method for determining the location of a wireless device comprisingthe steps of: (a) determining a first set of satellites for a region inwhich the wireless device is located; (b) transmitting first assistancedata to said device, said first assistance data including firstinformation from said first set of satellites; (c) attempting to measurefirst signals transmitted from one or more satellites in said first set;(d) determining a second set of satellites as a function of said firstsignals received from said first set of satellites; (e) transmittingsecond assistance data to said device, said second assistance dataincluding second information from said second set of satellites; (f)attempting to measure second signals transmitted from one or moresatellites in said second set; and (g) estimating a location of thedevice from said second signals.
 2. The method of claim 1 furthercomprising iteratively repeating steps (d) through (f) until said secondset of satellites is equal to or greater than a predetermined threshold.3. The method of claim 2 further comprising the step of combiningmeasurements of said second signals from one or more iterations to meetsaid predetermined threshold.
 4. The method of claim 1 wherein there isno intersection between the first set and second set of satellites. 5.The method of claim 1 wherein attempting to measure second signalsfurther comprises ensuring that said device does not attempt to measureone or more satellites in said first set having a measured first signal.6. The method of claim 1 further comprising the step of suppressingtransmissions of ones of said second assistance data if said secondassistance data was previously provided to said device.
 7. The method ofclaim 1 wherein said second set is selected as a function of coverageareas of said first signals from ones of said first set of satellites.8. The method of claim 1 wherein said second set is selected as afunction of one or more satellites that are not occluded by the Earthfrom said first signals from ones of said first set of satellites. 9.The method of claim 1 wherein the estimated location of the device is afunction of signals provided by a cellular network.
 10. The method ofclaim 1 wherein the satellites are part of a Global Navigation SatelliteSystem (“GNSS”).
 11. The method of claim 10 wherein the GNSS is selectedfrom the group consisting of: Global Positioning System (“GPS”),Galileo, GLONASS, and Quasi-Zenith Satellite System (“QZSS”).
 12. Themethod of claim 1 wherein the wireless device is selected from the groupconsisting of: cellular device, text messaging device, computer,portable computer, vehicle locating device, vehicle security device,communication device, and wireless transceiver.
 13. The method of claim1 wherein said region is selected from the group consisting of: aserving area of a base station serving said wireless device, anapproximate area of a communications network, a city, a municipality, acounty, a state, a country, a continent, and the Earth.
 14. The methodof claim 1 wherein said location is estimated as a function of apseudo-measurement.
 15. The method of claim 1 wherein determining asecond set of satellites further comprises including more or lesssatellites in said second set as a function of satellite elevation.